Theoretically long fins are dominant over short fin. But your actual outcome depends on their background. So youo will get long fins, in between fins and short fins. Percentage of Long fins should be bigger, but again, depends on background.

Usually the inbetweeners are short finned fish with kind of longer fins. So Im guessing they would pop up if both are pk carriers. They are pretty rare though. My fish came from a pk x hm(pk geno) all were either full pk or full long fin. no inbetweeners